Linux Virtualization - Mar 2023 - [PATCH vhost v3 04/11] virtio_ring: split: support premapped

virtio core only supports virtual addresses, dma is completed in virtio
core.

In some scenarios (such as the AF_XDP), the memory is allocated
and DMA mapping is completed in advance, so it is necessary for us to
support passing the DMA address to virtio core.

Drives can use sg->dma_address to pass the mapped dma address to virtio
core. If one sg->dma_address is used then all sgs must use
sg->dma_address, otherwise all must be null when passing it to the APIs
of virtio.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c8ed4aef9462..be2ff96964c3 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -70,6 +70,7 @@
 struct vring_desc_state_split {
 	void *data;			/* Data for callback. */
 	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
+	bool map_inter;			/* Do dma map internally. */
 };
 
 struct vring_desc_state_packed {
@@ -448,7 +449,7 @@ static void vring_unmap_one_split_indirect(const struct
vring_virtqueue *vq,
 }
 
 static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
-					  unsigned int i)
+					  unsigned int i, bool map_inter)
 {
 	struct vring_desc_extra *extra = vq->split.desc_extra;
 	u16 flags;
@@ -465,6 +466,9 @@ static unsigned int vring_unmap_one_split(const struct
vring_virtqueue *vq,
 				 (flags & VRING_DESC_F_WRITE) ?
 				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
 	} else {
+		if (!map_inter)
+			goto out;
+
 		dma_unmap_page(vring_dma_dev(vq),
 			       extra[i].addr,
 			       extra[i].len,
@@ -615,7 +619,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	struct scatterlist *sg;
 	struct vring_desc *desc;
 	unsigned int i, n, avail, descs_used, prev;
-	bool indirect;
+	bool indirect, map_inter;
 	int head;
 
 	START_USE(vq);
@@ -668,7 +672,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 		return -ENOSPC;
 	}
 
-	if (virtqueue_map_sgs(vq, sgs, total_sg, out_sgs, in_sgs))
+	map_inter = !sgs[0]->dma_address;
+	if (map_inter && virtqueue_map_sgs(vq, sgs, total_sg, out_sgs,
in_sgs))
 		return -ENOMEM;
 
 	for (n = 0; n < out_sgs; n++) {
@@ -734,6 +739,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 		vq->split.desc_state[head].indir_desc = desc;
 	else
 		vq->split.desc_state[head].indir_desc = ctx;
+	vq->split.desc_state[head].map_inter = map_inter;
 
 	/* Put entry in available array (but don't update avail->idx until they
 	 * do sync). */
@@ -759,7 +765,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	return 0;
 
 unmap_release:
-	virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);
+	if (map_inter)
+		virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);
 
 	if (indirect)
 		kfree(desc);
@@ -804,20 +811,22 @@ static void detach_buf_split(struct vring_virtqueue *vq,
unsigned int head,
 {
 	unsigned int i, j;
 	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
+	bool map_inter;
 
 	/* Clear data ptr. */
 	vq->split.desc_state[head].data = NULL;
+	map_inter = vq->split.desc_state[head].map_inter;
 
 	/* Put back on free list: unmap first-level descriptors and find end */
 	i = head;
 
 	while (vq->split.vring.desc[i].flags & nextflag) {
-		vring_unmap_one_split(vq, i);
+		vring_unmap_one_split(vq, i, map_inter);
 		i = vq->split.desc_extra[i].next;
 		vq->vq.num_free++;
 	}
 
-	vring_unmap_one_split(vq, i);
+	vring_unmap_one_split(vq, i, map_inter);
 	vq->split.desc_extra[i].next = vq->free_head;
 	vq->free_head = head;
 
@@ -839,8 +848,10 @@ static void detach_buf_split(struct vring_virtqueue *vq,
unsigned int head,
 				VRING_DESC_F_INDIRECT));
 		BUG_ON(len == 0 || len % sizeof(struct vring_desc));
 
-		for (j = 0; j < len / sizeof(struct vring_desc); j++)
-			vring_unmap_one_split_indirect(vq, &indir_desc[j]);
+		if (map_inter) {
+			for (j = 0; j < len / sizeof(struct vring_desc); j++)
+				vring_unmap_one_split_indirect(vq, &indir_desc[j]);
+		}
 
 		kfree(indir_desc);
 		vq->split.desc_state[head].indir_desc = NULL;
-- 
2.32.0.3.g01195cf9f

On Tue, Mar 21, 2023 at 05:34:59PM +0800, Xuan Zhuo
wrote:
> virtio core only supports virtual addresses, dma is completed in virtio
> core.
> 
> In some scenarios (such as the AF_XDP), the memory is allocated
> and DMA mapping is completed in advance, so it is necessary for us to
> support passing the DMA address to virtio core.
> 
> Drives can use sg->dma_address to pass the mapped dma address to virtio
> core. If one sg->dma_address is used then all sgs must use
> sg->dma_address, otherwise all must be null when passing it to the APIs
> of virtio.
> 
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> ---
>  drivers/virtio/virtio_ring.c | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c8ed4aef9462..be2ff96964c3 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -70,6 +70,7 @@
>  struct vring_desc_state_split {
>  	void *data;			/* Data for callback. */
>  	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
> +	bool map_inter;			/* Do dma map internally. */
I prefer a full name. E.g. "dma_map_internal". Eschew abbreviation.

>  };
>  
>  struct vring_desc_state_packed {
> @@ -448,7 +449,7 @@ static void vring_unmap_one_split_indirect(const struct
vring_virtqueue *vq,
>  }
>  
>  static unsigned int vring_unmap_one_split(const struct vring_virtqueue
*vq,
> -					  unsigned int i)
> +					  unsigned int i, bool map_inter)
>  {
>  	struct vring_desc_extra *extra = vq->split.desc_extra;
>  	u16 flags;
> @@ -465,6 +466,9 @@ static unsigned int vring_unmap_one_split(const struct
vring_virtqueue *vq,
>  				 (flags & VRING_DESC_F_WRITE) ?
>  				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
>  	} else {
> +		if (!map_inter)
> +			goto out;
> +
>  		dma_unmap_page(vring_dma_dev(vq),
>  			       extra[i].addr,
>  			       extra[i].len,
> @@ -615,7 +619,7 @@ static inline int virtqueue_add_split(struct virtqueue
*_vq,
>  	struct scatterlist *sg;
>  	struct vring_desc *desc;
>  	unsigned int i, n, avail, descs_used, prev;
> -	bool indirect;
> +	bool indirect, map_inter;
>  	int head;
>  
>  	START_USE(vq);
> @@ -668,7 +672,8 @@ static inline int virtqueue_add_split(struct virtqueue
*_vq,
>  		return -ENOSPC;
>  	}
>  
> -	if (virtqueue_map_sgs(vq, sgs, total_sg, out_sgs, in_sgs))
> +	map_inter = !sgs[0]->dma_address;
> +	if (map_inter && virtqueue_map_sgs(vq, sgs, total_sg, out_sgs,
in_sgs))
>  		return -ENOMEM;
>  
>  	for (n = 0; n < out_sgs; n++) {
> @@ -734,6 +739,7 @@ static inline int virtqueue_add_split(struct virtqueue
*_vq,
>  		vq->split.desc_state[head].indir_desc = desc;
>  	else
>  		vq->split.desc_state[head].indir_desc = ctx;
> +	vq->split.desc_state[head].map_inter = map_inter;
>  
>  	/* Put entry in available array (but don't update avail->idx until
they
>  	 * do sync). */
> @@ -759,7 +765,8 @@ static inline int virtqueue_add_split(struct virtqueue
*_vq,
>  	return 0;
>  
>  unmap_release:
> -	virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);
> +	if (map_inter)
> +		virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);
>  
>  	if (indirect)
>  		kfree(desc);
> @@ -804,20 +811,22 @@ static void detach_buf_split(struct vring_virtqueue
*vq, unsigned int head,
>  {
>  	unsigned int i, j;
>  	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
> +	bool map_inter;
>  
>  	/* Clear data ptr. */
>  	vq->split.desc_state[head].data = NULL;
> +	map_inter = vq->split.desc_state[head].map_inter;
>  
>  	/* Put back on free list: unmap first-level descriptors and find end */
>  	i = head;
>  
>  	while (vq->split.vring.desc[i].flags & nextflag) {
> -		vring_unmap_one_split(vq, i);
> +		vring_unmap_one_split(vq, i, map_inter);
>  		i = vq->split.desc_extra[i].next;
>  		vq->vq.num_free++;
>  	}
>  
> -	vring_unmap_one_split(vq, i);
> +	vring_unmap_one_split(vq, i, map_inter);
>  	vq->split.desc_extra[i].next = vq->free_head;
>  	vq->free_head = head;
>  
> @@ -839,8 +848,10 @@ static void detach_buf_split(struct vring_virtqueue
*vq, unsigned int head,
>  				VRING_DESC_F_INDIRECT));
>  		BUG_ON(len == 0 || len % sizeof(struct vring_desc));
>  
> -		for (j = 0; j < len / sizeof(struct vring_desc); j++)
> -			vring_unmap_one_split_indirect(vq, &indir_desc[j]);
> +		if (map_inter) {
> +			for (j = 0; j < len / sizeof(struct vring_desc); j++)
> +				vring_unmap_one_split_indirect(vq, &indir_desc[j]);
> +		}
>  
>  		kfree(indir_desc);
>  		vq->split.desc_state[head].indir_desc = NULL;
> -- 
> 2.32.0.3.g01195cf9f